Lead induced changes in the growth and antioxidant metabolism of the lead accumulating and non-accumulating ecotypes of Sedum alfredii

The phytotoxicity and antioxidative adaptations of lead （Pb） accumulating ecotype （AE） and non-accumulating ecotype （NAE） of Sedum alfredii Hance were investigated under different Pb treatments involving 0, 0.02 mmol/L Pb, 0.1 mmol/L Pb and 0.1 mmol/L Pb/0.1 mmol/L ethylenediaminetetraacetic acid （EDTA） for 6days. With the increasing Pb level, the Pb concentration in the shoots of AE plants enhanced accordingly, and EDTA supply helped 51% of Pb translocation to shoots of AE compared with those treated with 0.1 mmol/L Pb alone. Moreover, the presence of EDTA alleviated Pb phytotoxicity through changes in plant biomass, root morphology and chlorophyll contents. Lead toxicity induced hydrogen peroxide （H2O2） accumulation and lipid peroxidation in both ecotypes of S. alfredii. The activities of superoxide dismutase （SOD）, guaiacol peroxidase （G-POD）, ascorbate peroxidase, and dehydroascorbate reductase elevated in both leaves and roots of AE as well as in leaves of NAE with the increasing Pb levels, but SOD and G-POD declined in roots of NAE. Enhancement in glutathione reductase activity was only detected in roots of NAE while a depression in catalase activity was recorded in the leaves of NAE. A significant enhancement in glutathione and ascorbic acid （AsA） levels occurred in both ecotypes exposed to Pb and Pb/EDTA treatment compared with the control, however, the differences between these two treatments were insignificant. The dehydroascorbate （DHA） contents in roots of both ecotypes were 1.41 to 11.22-fold higher than those in leaves, whereas the ratios of AsA to DHA （1.38 to 6.84） in leaves altering more to the reduced AsA form were much higher than those in roots. These results suggested that antioxidative enzymes and antioxidants play an important role in counteracting Pb stress in S. alfredii.     

Comparison of EDTA- and Citric Acid-Enhanced Phytoextraction of Heavy Metals in Artificially Metal Contaminated Soil by Typha Angustifolia

A pot experiment was conducted to study the performance of EDTA and citric acid (CA) addition in improving phytoextraction of Cd, Cu, Pb, and Cr from artificially contaminated soil by T. angustifolia. T. angustifolia showed the remarkable resistance to heavy metal toxicity with no visual toxic symptom including chlorosis and necrosis when exposed to metal stress. EDTA-addition significantly reduced plant height and biomass, compared with the control, and stunted plant growth, while 2.5 and 5 mM CA addition induced significant increases in root dry weight. EDTA, and 5 and 10 mM CA significantly increased shoot Cd, Pb, and Cr concentrations compared with the control, with EDTA being more effective. At final harvest, the highest shoot Cd, Cr, and Pb concentrations were recorded in the treatment of 5 mM EDTA addition, while maximal root Pb concentration was found at the 2.5 mM CA treatment. However, shoot Cd accumulation in the 10 mM CA treatment was 36.9% higher than that in 2.5 mM EDTA, and similar with that in 10 mM EDTA. Shoot Pb accumulation was lower in 10 mM CA than that in EDTA treatments. Further, root Cd, Cu, and Pb accumulation of CA treatments and shoot Cr accumulation in 5 or 10 mM CA treatments were markedly higher than that of control and EDTA treatments. The results also showed that EDTA dramatically increased the dissolution of Cu, Cr, Pb, and Cd in soil, while CA addition had less effect on water-soluble Cu, Cr, and Cd, and no effect on Pb levels. It is suggested that CA can be a good chelator candidate for T. angustifolia used for environmentally safe phytoextraction of Cd and Cr in soils.     

Effects of soil amendments and EDTA on lead uptake by Chromolaena odorata: greenhouse and field trial experiments

Greenhouse and field trial experiments were performed to evaluate the use of Chromolaena odorata with various soil amendments for phytoextraction of Pb contaminated soil Pb mine soils contain low amount of nutrients, so the additions of organic (cow manure) and inorganic (Osmocote and NH4NO3 and KCl) fertilizers with EDTA were used to enhance plant growth and Pb accumulation. Greenhouse study showed that cow manure decreased available Pb concentrations and resulted in the highest Pb concentration in roots (4660 mg kg(-1)) and shoots (389.2 mg kg(-1)). EDTA increased Pb accumulation in shoots (17-fold) and roots (11-fold) in plants grown in soil with Osmocote with Pb uptake up to 203.5 mg plant(-1). Application of all fertilizers had no significant effects on relative growth rates of C. odorata. Field trial study showed that C. odorata grown in soil with 99545 mg kg(-1) total Pb accumulated up to 3730.2 and 6698.2 mg kg(-1) in shoots and roots, respectively, with the highest phytoextraction coefficient (1.25) and translocation factor (1.18). These results indicated that C. odorata could be used for phytoextraction of Pb contaminated soil. In addition, more effective Pb accumulation could be enhanced by Osmocote fertilizer. However, the use of EDTA in the field should be concerned with their leaching problems.     

一种新的铅富集植物--富集生态型东南景天

对浙江一古老铅锌矿区的土壤和植物种群进行调查后发现一种新的具有耐铅特性和铅富集能力的植物--景天科景天属东南景天(Sedum alfredii Hance),称为铅富集生态型植物.进一步比较和分析了不同浓度硝酸铅处理对富集和非富集生态型东南景天的生长及其对铅的吸收特性的影响.结果表明, 320 mg Pb/L处理对富集生态型的地上部分生长无显著影响,而非富集生态型在20 mg Pb/L时即出现受害症状.富集和非富集生态型的地上部分铅含量、根系铅含量以及单株铅积累速率均随处理浓度的增加而表现出先升后降的变化趋势.其中富集生态型的地上部分铅含量、根系铅含量以及单株铅积累速率最高可达到514 mg/kg、13 922 mg/kg和8.62 μg/plant/d,分别是非富集生态型的2.27、2.62和7.16倍.由于具有生长速度快和高积累铅的能力,从植物修复的观点来说,东南景天铅富集生态型在铅污染土壤的修复方面具有巨大的潜力.     

Phytoextraction of Pb and Cu contaminated soil with maize and microencapsulated EDTA

Chelate-assisted phytoextraction using agricultural crops has been widely investigated as a remediation technique for soils contaminated with low mobility potentially toxic elements. Here, we report the use of a controlled-release microencapsulated EDTA (Cap-EDTA) by emulsion solvent evaporation to phytoremediate soil contaminated with Pb and Cu. Incubation experiments were carried out to assess the effect of Cap- and non-microencapsulated EDTA (Ncap-EDTA) on the mobility of soil metals. Results showed EDTA effectively increased the mobility of Pb and Cu in the soil solution and Cap-EDTA application provided lower and more constant water-soluble concentrations of Pb and Cu in comparison with. Phytotoxicity may be alleviated and plant uptake of Pb and Cu may be increased after the incorporation of Cap-EDTA. In addition phytoextraction efficiencies of maize after Cap- and Ncap-EDTA application were tested in a pot experiment. Maize shoot concentrations of Pb and Cu were lower with Cap-EDTA application than with Ncap-EDTA. However, shoot dry weight was significantly higher with Cap-EDTA application. Consequently, the Pb and Cu phytoextraction potential of maize significantly increased with Cap-EDTA application compared with the control and Ncap-EDTA application.     

Effect of Pb on leaf antioxidant enzyme activities and ultrastructure of the two ecotypes of <Emphasis Type="Italic">Sedum alfredii</Emphasis> Hance

Hydroponic experiments were conducted to study the effect of Pb on growth, leaf antioxidant enzyme activities, and ultrastructure of the accumulating ecotype (AE) and non-accumulating ecotype (NAE) of Sedum alfredii Hance. AE was found to be more tolerant to excessive Pb levels in growth medium. Concentrations of Pb in the shoots of the AE were 1.98 times higher than those in the NAE when 0.2 mM Pb was supplied. Both chlorophyll a and b did not decrease significantly in AE plants after Pb treatment, while a significant decrease was noted in chlorophyll a and b of NAE plants treated with Pb concentrations greater than 0.05 mM. The results showed that activities of superoxide dismutase (SOD) and catalase (CAT) were elevated in the leaves of AE under Pb stress. However in NAE, Pb-caused enhancement was noticed only in the activity of SOD while activity of CAT was declined as compared to the control plants. With increased Pb level, malondialdehyde (MDA) content increased significantly in both ecotypes of S. alfredii, indicating that Pb toxicity led to lipid peroxidation and membrane damage, but MDA content in the leaves of NAE was always higher than in AE plants. The ultrastructural analysis of the spongy mesophyll cells revealed that excessive Pb concentrations obviously damaged the cell membrane, chloroplasts, and mitochondria of both the ecotypes but damage was more severe in NAE. Although growth, leaf physiology, and ultrastructure of both the ecotypes were affected by Pb treatment, deleterious effects were more pronounced in NAE. This text was submitted by the authors in English.     

Chemically enhanced phytoextraction of risk elements from a contaminated agricultural soil using Zea mays and Triticum aestivum: performance and metal mobilization over a three year period

Enhanced phytoextraction using EDTA for the remediation of an agricultural soil contaminated with less mobile risk elements Cd and Pb originating from smelting activities in Príbram (Czech Republic) was assessed on the laboratory and the field scale. EDTA was applied to the first years crop Zea mays. Metal mobilization and metal uptake by the plants in the soil were monitored for two additional years when Triticum aestivum was planted. The application ofEDTA effectively increased water-soluble Cd and Pb concentrations in the soil. These concentrations decreased over time. Anyhow, increased concentrations could be still observed in the third experimental year indicating a low possibility of groundwater pollution after the addition of EDTA during and also after the enhanced phytoextraction process under prevailing climatic conditions. EDTA-applications caused phytotoxicity and thereby decreased biomass production and increased Cd and Pb uptake by the plants. Phytoextraction efficiency and phytoextraction potential were too low for Cd and Pb phytoextraction in the field in a reasonable time frame (as less than one-tenth of a percent of total Cd and Pb could be removed). This strongly indicates that EDTA-enhanced phytoextraction as implemented in this study is not a suitable remediation technique for risk metal contaminated soils.     

Phytoremediation of arsenic and lead in contaminated soil using Chinese brake ferns (Pteris vittata) and Indian mustard (Brassica juncea)

Field and greenhouse experiments were performed to assess the performance of phytoremediation of arsenic and lead from contaminated soil at an EPA Superfund site (Barber Orchard). Chinese Brake ferns (Pteris vittata) were used to extract arsenic. On average, fern shoot arsenic concentrations were as high as 20 times the soil arsenic concentrations under field conditions. It was estimated that 8 years would be required to reduce the acid-extractable portion of soil arsenic to safe levels (40 mg/kg). The effect of soil pH on arsenic extraction was also investigated. Results indicate that increasing soil pH may improve arsenic removal. Indian mustard plants (Brassica juncea) were used under greenhouse conditions to phytoextract soil lead. EDTA was applied to soil and was found to improve lead extraction. When the EDTA concentration was 10 mmol EDTA/kg soil in soil containing 338 mg Pb/kg soil, mustard plants extracted approximately 32 mg of lead. In conclusion, phytoremediation would be a suitable alternative to conventional remediation techniques, especially for soils that do not require immediate remediation.     

Investigation of Arbuscular mycorrhizal Fungus and EDTA Efficiencies on Lead Phytoremediation by Sunflower in a Calcareous Soil

Lead (Pb) contamination of soils is a widespread problem. Mycorrhizal inoculation and synthetic chelators such as ethylenediaminetetraacetic acid (EDTA) may be useful for improving phytoremediation efficiency in Pb-contaminated soils. A greenhouse experiment was performed to study the influence of inoculation with arbuscular mycorrhizal fungus (AMF), Glomus mosseae, and addition of EDTA on phytoremediation of Pb by sunflowers (Helianthus annuus) in a calcareous soil. The experiment was a completely randomized design in a factorial arrangement with five levels of Pb, two levels of mycorrhizal treatments, and two levels of EDTA. Inoculation increased root colonization as Pb levels increased, but the addition of EDTA decreased it. Shoot and root dry matter yields increased by inoculation; however, they decreased with EDTA and Pb levels in co-application treatments. Pb concentration in shoots was significantly higher than that in roots, indicating a translocation factor greater than 1. Inoculation or addition of EDTA significantly increased Pb in roots and its translocation to shoots. The uptake index (UI) value increased in co-application of EDTA and AMF and the individual application of them; it is, therefore, concluded that both AMF and EDTA are effective in phytoremediation of Pb by sunflowers in the studied soil.     

Soil flushing of a sandy loam contaminated with Pb(II), PbS4 (s), PbCO3 (3), or Pb‐Naphthalene: Column results

Column‐scale oil flushing of a sandy loam contaminated with either Pb(II) (500 mg/kg Pb), PbSO₄ (10,000 mg/kg Pb), PbCO₃ (10,000 mg/kg Pb), or Pb‐naphthalene (400 mg/kg Pb, 333 mg/kg naphthalene) was investigated. HCl (0.1 N), EDTA (0.01 M), and CaCl₂ (1.0 M) were selected as the soil‐flushing solutions based on soil‐washing experiments. For the Pb‐only tests, Pb removal efficiencies were 85, 100, and 78% for HCl, EDTA, and CaCl₂, respectively. For PbSO₄ (s), Pb removal efficiencies were 32, 100, and 96% for HCl, EDTA, and CaCl₂, respectively, and for PbCO₃ were 97, 100, and 14% for HCl, EDTA, and CaCl₂, respectively. Larger amounts of flushing solutions were required for the remediation of PbSO₄‐and PbCO₃‐contaminated soils compared with the Pb‐only tests, most likely because of slower dissolution kinetics and the neutralization of HCl by CO₃ ^‐2 For Pb‐naphthalene, Pb removal efficiencies were 78 and 72% for HCl and EDTA, respectively, which compared well with soil‐washing results but were less than those observed in Pb‐only column studies.     

Solubility and accumulation of metals in Chinese brake fern, vetiver and rostrate sesbania using chelating agents

Greenhouse experiments were conducted to study the effects of chelating agents on the growth and metal accumulation of Chinese brake fern (Pteris vittata L.), vetiver (Vetiveria zizanioides L.), and rostrate sesbania (Sesbania rostrata L.) in soil contaminated with arsenic (As), Cu, Pb, and Zn. Among the five chelating agents used [ethylenediaminetriacetic acid (EDTA), hydroxyethylenediaminetriacetic acid (HEDTA), nitrilotriacetic acid (NTA), oxalic acid (OA), and phytic acid (PA)], OA was the best to mobilize As, EDTA to mobilize Cu and Pb, and HEDTA to mobilize Zn from soil, respectively. The biomass of vetiver was the highest, followed by rostrate sesbania. All chelating agents inhibited the growth of Chinese brake fern and rostrate sesbania, but HEDTA significantly increased the aboveground biomass of vetiver. Dry weights of both Chinese brake fern and rostrate sesbania decreased with increasing EDTA concentrations amended in the soil, especially in treatments with high EDTA concentrations. EDTA and HEDTA enhanced Cu, Zn, and Pb, but lowered As accumulation in all three plant species, except for As in vetiver, while OA significantly enhanced As accumulation in the aboveground part of vetiver. Concentrations of Cu, Zn, and Pb in the aboveground parts of plants increased significantly with the increase of EDTA concentrations and treatment time. In addition to As, Chinese brake fern also accumulated the highest Cu, Pb, and Zn in its aboveground parts among the three plant species grown in metal-contaminated soil with EDTA/HEDTA treatments. This species, therefore, can be used to simultaneously clean up As, Cu, Pb, and Zn from contaminated soils with the aid of EDTA or HEDTA.     

Role of EDTA in alleviating lead toxicity in accumulator species of Sedum alfredii H

The effects of Pb chelater (EDTA-Pb) and ionic Pb (Pb(NO(3))(2)) on root cell death, Pb accumulation, changes of ROS, activities of antioxidant enzymes and uptake of mineral elements in response to Pb toxicity in Sedum alfredii H. were compared. Loss of plasma membrane integrity became serious by increasing Pb concentration in the medium, 200 microM Pb + 200 microM EDTA has alleviated the root cell death. The biomass was significantly affected by high concentration of Pb, and root growth was also affected by EDTA-Pb compared with ionic Pb. Lead accumulation was higher in the samples treated with ionic lead than that of the control. The concentration of reactive oxygen species (ROS) was determined by fluorescence microscopy, which indicates that the Pb stress increased the content of ROS significantly, whereas the EDTA-Pb decreased the burst of H(2)O(2). High Pb concentrations increase the activity of SOD and LOX. The Cu concentration in root increased significantly under Pb and EDTA-Pb treatment, and 200 microM Pb markedly increased the Fe content in roots. Under ionic Pb condition, the contents of Mg, Ca and K in shoots decreased, whereas they were significantly increased in case of EDTA-Pb. These results suggested that accumulating ecotype of S. alfredii roots were inefficient in uptake of higher concentration of EDTA-chelated Pb for long treatment duration, and that lead toxicity could be alleviated by EDTA.     

Stabilization of Oxidic Tailings and Contaminated Soils by Calcium Oxyphosphate Addition: The Case of Montevecchio (Sardinia,Italy)

The effectiveness of an in situ heavy metals fixation technique aimed at converting contaminants to low solubility and low bioavail-ability forms, eliminating the risk posed by oxidic tailings and contaminated soils, was investigated. Calcium oxyphosphate salt (Ca(H₂PO₄)₂·H₂O) was used as a stabilizing agent for oxidic tailings and contaminated soils originating from Montevecchio, Sardinia, Italy. Stabilization was effected by mixing the contaminated soil or oxidic tailing sample with calcium oxyphosphate salt at various doses. The effectiveness of stabilization was evaluated by USEPA TCLP standard toxicity testing. Complementary EDTA extraction tests and biological tests using beans Phaseolous vulgaris as plant indicator were carried out. The toxicity of Pb and Cd was reduced below TCLP regulatory limits at calcium oxyphosphate doses higher than 0.7 and 0.2% w/w for soils and tailings, respectively. Lead solubility according to the EDTA test decreased with phosphate dose for both materials tested. Lead uptake by plant leaves and roots from the soil sample decreased with the phosphate addition, while Cd uptake remained almost constant. An adverse effect on plant growth and Zn uptake was observed for calcium oxyphosphate dose up to 1.1% w/w. Based on the results, a remediation scheme for oxidic tailings and contaminated soils is proposed.     

Soil amendment application frequency contributes to phytoextraction of lead by sunflower at different nutrient levels

Phytoextraction has been proposed as an alternative remediation technology for soils polluted with heavy metals, but is generally perceived to be too slow. Enhancing accumulation of trace pollutants in harvestable plant tissues is a prerequisite for such technology to be practical. The main aims of this paper were to investigate whether a combination of nutrients and ethylenediaminetetraacetic acid (EDTA) enhanced Pb uptake of sunflower (Helianthus annuus) plants, and if timing of EDTA application altered Pb uptake and environmental persistence. Plants were grown in greenhouse pot experiments. Pb distributions and uptake of the whole plant were studied using chemical and flame atomic absorption spectrometry analyses. Pb mobilization by EDTA appeared to be dose dependent, with more mobilization for the high than the low dose. There were distinct differences in mobilization patterns of various nutrient amendments. EDTA mobilized Pb more in the medium than the highest and lowest nutrient levels. Heterogeneous soil humus components exerted mobilizing and stabilizing effects, so the medium nutrition was most effective for phytoextraction. At low nutrient levels, Pb concentration in the shoot with one low EDTA application was less than two applications to the same total EDTA dosage. So in the poor soil, two applications of EDTA was more effective than once. The half-life of two low EDTA treatment applications was longer than for one application, to the same total dosage. In general, sunflower was suited to phytoremediation of moderately Pb-contaminated soil by phytoextraction.     

Screening of Indigenous Ornamental Species from Different Plant Families for Pb Accumulation Potential Exposed to Metal Gradient in Spiked Soils

Contamination of surface soils with lead (Pb) is a global concern due to the release of hazardous materials containing the metal element. In order to explore ways to remediate contaminated soils with less impact on environment and costs, this study aimed at screening ornamental plant species exposed to Pb gradient in spiked soils for Pb phytoextraction. Twenty-one ornamental plant species that currently grow in Pakistan, were selected to assess their potential for Pb accumulation. Pot experiments were conducted to evaluate the accumulative properties of the different plant species in unspiked control (Pb = 0) and spiked soils with different levels of Pb at 500, 1000, 1500 and 2000 mg Pb kg^?1 of soil. Biotranslocation factor (TF), Enrichment factor (EF) and Bioconcentration factor (CF) were calculated to assess the phytoremediation potential of tested plant species after seven weeks of exposure. Out of 21 plant species, Pelargonium hortorum and Mesembryanthemum criniflorum performed better and accumulated more than 1000 mg Pb kg^?1 of shoot dry biomass when they were grown in 500, 1000 and 1500 mg Pb kg^?1 contaminated soils. Both plants had no significant (P < 0.05) variation in the total dry biomass with increasing soil Pb concentration indicating a high tolerance to Pb. Considering the capacity of Pb accumulation, total dry biomass, TF, EF &; CF indices, Pelargonium hortorum and Mesembryanthemum criniflorum could be considered as Pb hyperaccumulators and could have the potential to be used in phytoremediation.     

How phytohormone IAA and chelator EDTA affect lead uptake by Zn/Cd hyperaccumulator Picris divaricata

In this paper, the effects of indole-3-acetic acid (IAA) and/or ethylenediaminetetraacetic acid (EDTA) on lead uptake by a Zn/Cd hyperaccumulator Picris divaricata were studied. P. divaricata responded to Pb by better root system and increased biomass in presence of phytohormone IAA, which was able to reduce the inhibiting effects of Pb on transpiration without reducing the uptake of Pb The application of 100 microM IAA increased plant transpiration rate by about 20% and Pb concentration in leaves by about 37.3% as compared to treatment exposed to Pb alone. The enhanced phytoextraction efficiency could be attributed to the mechanisms played by IAA through alleviating Pb toxicity, creating better root system and plant biomass, promoting a higher transpiration rate as well as regulating the level of nutrient elements. On the contrary, inefficiency of phytoextraction was found with EDTA or the combination of IAA and EDTA probably because most Pb was in the form of Pb-EDTA complex which blocked the uptake by P. divaricata. The present study demonstrated that IAA was able to enhance the phytoextraction of Pb by Zn/Cd hyperaccumulator P. divaricata, providing a feasible method for the phytoremediation of polymetallic contaminated soils.     

The effect of EDTA and EDDS on lead uptake and localization in hydroponically grown Pisum sativum L.

Pisum sativum plants were treated for 3 days with an aqueous solution of 100 μM Pb(NO₃)₂ or with a mixture of lead nitrate and ethylenediaminetetraacetic acid (EDTA) or [S,S]-ethylenediaminedisuccinic acid (EDDS) at equimolar concentrations. Lead decline from the incubation media and its accumulation and localization at the morphological and ultrastructural levels as well as plant growth parameters (root growth, root and shoot dry weight) were estimated after 1 and 3 days of treatment. The tested chelators, especially EDTA, significantly diminished Pb uptake by plants as compared to the lead nitrate-treated material. Simultaneously, EDTA significantly enhanced Pb translocation from roots to shoots. In the presence of both chelates, plant growth parameters remained considerably higher than in the case of uncomplexed Pb. Considerable differences between the tested chelators were visible in Pb localization both at the morphological and ultrastructural level. In Pb+EDTA-treated roots, lead was mainly located in the apical parts, while in Pb+EDDS-exposed material Pb was evenly distributed along the whole root length. Transmission electron microscopy and EDS analysis revealed that in meristematic cells of the roots incubated in Pb+EDTA, large electron-dense lead deposits were located in vacuoles and small granules were rarely noticed in cell walls or cytoplasm, while after Pb+EDDS treatment metal deposits were restricted to the border between plasmalemma and cell wall. Such results imply different ways of transport of those complexed Pb forms.     

Comparison of organic and inorganic amendments for enhancing soil lead phytoextraction by wheat (Triticum aestivum L.)

Phytoextraction has received increasing attention as a promising, cost-effective alternative to conventional engineering-based remediation methods for metal contaminated soils. In order to enhance the phytoremediative ability of green plants chelating agents are commonly used. Our study aims to evaluate whether, citric acid (CA) or elemental sulfur (S) should be used as an alternative to the ethylene diamine tetraacetic acid (EDTA)for chemically enhanced phytoextraction. Results showed that EDTA was more efficient than CA and S in solubilizing lead (Pb) from the soil. The application of EDTA and S increased the shoot biomass of wheat. However, application of CA at higher rates (30 mmol kg(-1)) resulted in significantly lower wheat biomass. Photosynthesis and transpiration rates increased with EDTA and S application, whereas these parameters were decreased with the application of CA. Elemental sulfur was ineffective for enhancing the concentration of Pb in wheat shoots. Although CA did not increase the Pb solubility measured at the end of experiment, however, it was more effective than EDTA in enhancing the concentration of Pb in the shoots of Triticum aestivum L. It was assumed that increase in Mn concentration to toxic levels in soil with CA addition might have resulted in unusual Pb concentration in wheat plants. The results of the present study suggest that under the conditions used in this experiment, CA at the highest dose was the best amendment for enhanced phytoextraction of Pb using wheat compared to either EDTA or S.     

Heavy metal impact on bacterial biomass based on DNA analyses and uptake by wild plants in the abandoned copper mine soils

The metals contamination in surface soils and their accumulation in wild plants from the abandoned Burra and Kapunda copper mines located in South Australia were assessed, and the predominant bacterial diversity in the contaminated surface soils from these two abandoned copper mine sites were evaluated through polymerase chain reaction–denaturing gradient gel electrophoresis (PCR-DGGE) analysis. The results showed the average concentration of Cu in soils was 3821.59 mg/kg while wild plants accumulated up to 173.44 mg/kg. The concentration of Cu in shoots of spear grass (Stipa uitida) and berry saltbush (Afriplex semibaccata) was higher than that of roots. The concentration of total and extractable As, Cd, Cu and Pb in soils slightly correlated with of these elements in the corresponding wild plants. The toxicity of Cu in heavily contaminated soils impacted on the quantities of specific microbial populations and no significant change in the microbial diversity of highly contaminated soils.     

LEAD PHYTOEXTRACTION BY WHEAT IN RESPONSE TO THE EDTA APPLICATION METHOD

Lead solubilization in soil and accumulation by spring wheat (Triticum aestivum L.) was studied in response to the ethylenediaminetetraacetic acid (EDTA) application method. In this study, 4 mmol EDTA kg^?1 was applied using two application methods (a single dose and split doses) either alone or in combination with elemental sulfur. Results indicate that the application of EDTA in four equal splits at 1 mmol kg^?1 during the growth period resulted in significantly higher shoot dry matter than its application at 4 mmol kg^?1 at once 10 d before harvesting the wheat crop at the bolting stage. EDTA applied in split doses resulted in less lead (Pb) solubilization as compared with the single-dose application. The split application also significantly increased the shoot Pb concentration and Pb accumulation by wheat shoots as compared with the single-dose application. Despite its lesser effect on Pb solubilization, the EDTA application in split doses substantially increased Pb accumulation; thus, it is expected to minimize the risk of groundwater contamination.